The investigation into the recovery of a firecracker from a Kingfisher aircraft that arrived here from Bangalore on Sunday is centred on the loaders engaged by the private agency that handles the cargo of the airline in Thiruvananthapuram.

The loaders, especially those who were on duty then, are under the surveillance of the city police. The Bangalore police have ruled out chances of the firecracker entering the rear cargo hold area of the ATR-72 aircraft at the Bangalore international airport.

The police are keeping a close watch on six loaders who were on duty and the other five on the rolls of the agency. Sources said the police searched their houses as they were the only ones who had access to the aircraft besides the designated airline staff.

The fact that the firecracker was wrapped in a Malayalam newspaper and SSLC question papers support the theory that it might have been planted in Thiruvananthapuram.

Police sources say they are yet to come to any conclusion on how the firecracker was placed in the cargo hold area of the aircraft.

A team led by City Police Commissioner M.R. AjithKumar that had gone to Bangalore on Sunday to probe the incident returned on Monday.

Sources say the team, comprising Assistant Commissioners K.C. Sasikumar and K.E. Baiju, questioned the airline staff and loaders engaged by the airline in Bangalore. The team watched the CCTV footage at the Bangalore airport and took statements of the passengers who were on the flight.

A three-member team of the Bangalore police arrived here as part of the investigation into the incident. The team reportedly questioned the airline staff and the loaders here. Though the firecracker, weighing 10-15 gm., was not powerful enough to blow up the aircraft or cause any other damage, the incident has been labelled by the Civil Aviation Ministry as a major security lapse.

The chemical analysis of the firecracker has revealed that it contained sulphur, aluminium powder and potassium chlorate.

Meanwhile, security has been stepped up at the airport. A meeting presided over by airport director V.N. Chandran on Monday reviewed the security arrangements. All airlines and user agencies have been asked to be vigilant.

K.V. Subramanya writes from Chickballapur: The Bureau of Civil Aviation Security (BCAS) is yet to find a clue on how a packet containing a firecracker made its way into the Kingfisher aircraft.

A team of officials from BCAS, New Delhi, arrived at the Bengaluru International Airportan at Devanahalli near here on Monday to investigate the incident, which has raised concerns about aviation safety and security.

Sources in the Central Industrial Security Force (CISF), which provides airside security at airports, told The Hindu that investigations by the BCAS were still to make any headway.

Incidentally, passengers and their baggage are allowed inside the terminal building at the BIA without any screening.